Capacitors are typically comprised of a pair of opposing conductive electrodes which are separated by one or more dielectric materials. A continuing goal in semiconductor circuitry fabrication is to shrink individual devices to increase circuit density and thereby the amount of circuitry which can be fit into a given space. Such can be achieved by both reducing the area over the substrate consumed by an individual device as well as in reducing its thickness.
One factor affecting a capacitor's construction and operation is breakdown voltage. Breakdown voltage is that voltage which causes the capacitor to form a conductive short between the electrodes through the dielectric material, thereby destroying the capacitor. It is function of the composition of the dielectric material as well as it thickness, among other factors. Generally if the inherent breakdown voltage of a given material can be increased, thickness of a capacitor dielectric layer for a given application could be reduced.
Silicon dioxide, silicon nitride and silicon oxynitride continue to find use as capacitor dielectric materials. One common composite of these materials utilized in capacitors as the dielectric layer is an oxide-nitride-oxide material commonly referred to as ONO. The first formed oxide layer comprises silicon dioxide typically formed by native oxidation of an oxidizable first or lower capacitor electrode comprising, for example, conductively doped polysilicon. Such typically produces a silicon dioxide layer approximately 20 Angstroms thick. Subsequently, a silicon nitride layer is deposited, such as by combining dichlorosilane and ammonia in a low pressure chemical vapor deposition reactor at 650.degree. C. Such layer as deposited may not be as dense as desired. Accordingly, the silicon nitride layer is subjected to an oxidation step to densify and fill any pinholes inherent in the deposition which produces such layer. An example oxidation step flows equal amounts of H.sub.2 and O.sub.2 at atmospheric pressure and 800.degree. C. This transforms the outer 20 Angstroms or so of the silicon nitride layer into a silicon oxynitride material, typically designated as SiO.sub.x N.sub.y. This layer is what typically constitutes the outer "O" of the ONO capacitor dielectric layer or material.
Accordingly, it would be desirable to develop techniques and materials which inherently result in increased breakdown voltage of ONO capacitors, and silicon oxynitride capacitor dielectric layers particularly.